Regenerative indicating system



Patented July 9, 1946 OFFICE- John A. Rankin, Port Washington, Y., yassignor to -Radio Corporation of America,

of Delaware a corporation application Augustzz, 1941, lseriali No. 407,966

This invention relates to a radiant energy fregenerative feed back system for use'between two or more movable vehicles, such as airplanes'tanks, trucks, ships, or combinations of such craft.' 1

It is desirable in, wartime thatr two-for imorel friendly airplanes be ableto .identityrthemselves to one another duringlig'htfi'with` a system'having a limited range of'ftransmissionysuch-that more' remotely located enemyifstationsvmay not be apprized of the presence of theiplanes:v The present invention provides a system/by means of which two or more friendly airplanes; equipped with identical apparatus, can provide'a char'- acteristic indication when flying withinthe eec'- tive range of transmission. By means'ofthis'invention, the pilot of a combat plane-isimmediately able to determine wlfietheranr approaching craft is a friend or a foe. i. 1' I The present invention finds furtheruse inicon'- nection with truck convoys, where itisv essential during war conditions that trucks be ableatozfollow one another in the dark without losingco'ntact or colliding with each other By means of the present invention there is provided a system for' determining not only whether one truck-is immediately behind another truck in -the-convoy, but also the approximate distance v"between'-ad'- jacent trucks'. 'f A' more detailed description of the invention follows in conjunction with a drawing; wherein-t Fig. 1 illustrates diagrammatically the-applica'- tion of the invention'to a pair Ao1 airplanes; I

Figs. 2 and 3 showin detail 'one ernbc'ic'imentl of the circuit which can beu'se'd on eachplan'e; both for identication purposesand for determining the relative distance between'planes; and Fig. 4 illustrates diagrammatically the vapplication of the invention to an automobile' truck Referring to Fig. 1in moredet'ail, therey isshbwn a pair of airplanes (for exampl'eg'combatplanes) I and 2, each of 'which is 'providedfwithsuitable radiating apparatus comprising van oscillatorf, an amplifier It, a transmitting-antennaAl; and a receiving antenna A2. The antennas Aifand'Az are arranged in a manner to reducethecupling between them substantiallytof zero. Q'I'he reason for this is to prevent sueli' feedback betweenthe transmitting and' receiving antennas' of each plane which will produce regeneration. Oneway by which this may be. accomplished is: to position the antennas' A1 and Ae ini.a;vertical line with the metallic body of thezplane locatedibetween them. These antennasmay be ofi any suitable form, although it is preferred; in the arrangement shown in the drawing, that each antennafbefonee 4i1. cnims. (01;.2504-25 j` quarter wavelength long at the operating'frequency. Obviously,r fthe body of the-plane-is made ofA metal, the antenna shouldbeY suitably Y insulated from the plane'at their pointsfiof supportyif the bodyof the plane is madeofplastic materialor other ysuitable insulation, the antennas canrbe positioned in-known 1manner to minimize coupling between them. 'I'heoscillator i8 in each ,plane`v is A-preferably av constanty frequency ,type, Y

suchas ,a1 crystal oscillator, supplying energy t0 be'amplified by apparatus 'v 4 and radiated from thetransmitting antenna A1. Thesys'temjis s o designedthat Athe Waves radiated by eachtransr `mitting antenna isf-relatively weak in intensity and-inayibeeiective within averylimited range.

For-airplanes, sucha-range mightv be,f'perhapsfV 'T500-yards; in-order to'enable thexpilotffto determinegwit-hin a'short time before an approaching Y craft comeswithin e'iective firing range?WhetherVV the approaching craft-is a friend or' afoe.

withthesystem as thus-S0 fardeseribed, unie airplaneis a friend and is equippedidentically asairplane l, Ytheradiated wave from the'transrnittirigantennar A1 ofp'lane` lv will-be received on the'reoeivin'g antenna A2 of plane 2; amplied in: apparatus ifin 1 plane 2, and theV amplified wavesl transmitted over' transmitting. antenna TA1 :0f planeV L and received on' receiving'antennazAz ofV planer l, thus providingia regenerative" feed back circuit lbetween'the'" two planes. As the planesfapproa'cli each other, the loverall radiation couplinginwthis vfeed Vback circuiti will increase,

therebyincreasing the amplitude@oftheV radiated,` waves to an extent necess'ary'to providey 'a suit:- i

ableindi'c'ationto the pilot. Obviously, 'therapparatus in both planes are not only: identical but should'operate at 'the' same frequency.

VIf the pilot 'cfa plane equipped with the inven'` Y tion findsithat the approaching craft is within tiie'rrange in'which hisradio equipment should Y,

increase in intensity of output, but doesv not do so, the` pilot' will immediately' realize that the api-A proachingcraft'is a foe and will'take suitable necessary: Lookinfgatlit 'another wayfwe can say thatftheapparatus'in theftwoy "planes l and 2;

taken'fto'gtirerl constitute a singleoscillator Vcire cuitfwnenj ioated (within a, distance `to provide suitable regenerative feed back' betweenftheftwo pianesl.. The distance at? which self-oscillations take-'place may be controlled by changing the gain .ofthe ampliers IU; that'is,fasthe gain'- is increased in both amplifiers lll', the distance be-k tween 'the planes may likewise be increased and still' provide the desired regeneratve'feed back.,

Each of the planes I and 2 is preferably provided with a suitable indicating device, such as a lamp or an alarm to indicate when self-oscillation or increased intensity of output takes place, which will occur only when another craft, identically equipped, is within the range to provide regenerative feed back.

Fig. 2 shows, by way of example only, one circuit arrangement for the radio apparatus of planes I and 2. In Fig. 2 there is shown an amplifying circuit comprising a pair of vacuum tubes I and I I arranged in cascade and positioned between a receiving antenna -Az and a transmitting antenna A1. The reeciving antenna Az is shown coupled to a tuned input circuit I3 connected between the grid and cathode of the rst vacuum tube amplifier I0. This vacuum tube is shown as being of the multi-grid type, although, if desired, a triode or a four-element tube can be used instead. The anode of the vacuum tube I0 is connected to a parallel tuned output circuit I5 to which is coupled another parallel tuned circuit IS constituting the input circuit for the multigrid vacuum tube I I. The anode of vacuum tube II is connected to another parallel tuned circuit I'I which is the output for amplifier I I and which is coupled to the transmitting antenna A1. A local oscillator I8 of the Hartley type is shown coupled to the tuned circuit I5 by means of coupling circuit 26 by virtue of which the oscillations generated by this oscillator are ampliiied in II and radiated from antenna A1 in a relatively weak transmission. The parallel tuned circuits I3, I5, I6 and I1 are tuned to the same frequency of operation, which is also the same frequency of operation as antennas A1 and Az. These antennas are shown as dipoles having an overall length of preferably a half wavelength at the operating frequency and so arranged with respect to one another that there is substantially no coupling between them. To reduce the feed back between antennas A1 and A2 to a minimum, one may use the usual known expedients of providing a shield between the antennas, which shield may take the form of the metallic body of a plane as hereinabove described in connection with Fig. 1. The advantage of coupling the oscillator I8 to the tuned circuit I5 is that the output of the oscillator is amplified by vacuum tube I I only and radiated overfAi and cannot react back upon the receiving antenna Az through the vacuum tube I0. By way of example, the amplifying stage I0 might be arranged to give a gain oi 100 while the second vacuum tube stage Il might be arranged to give a gain of ten, thus providing an overall gain of 1000between antennas A2 and A1.

In order to provide a suitable indication to the pilot of a plane, there are provided a pair of relays I9 and 20 arranged electrically in series relation and connected between the grid and cathode of the vacuu-m tube I I. Normally, when there is no regenerative feed back path provided by another vehicle equipped identically with the apparatus of Fig. 2, the armatures of the relays I9 and 20 will be in the positions indicated in the drawing and maintained this way by means of springs 2I, 2|. In this position, the amber lamp 22 will be lighted over a path traced from the positive terminal of battery 23 through the iilament of lamp 22, through the upper two contacts on the armature of relay I9 as closed by the armature, and back to the negative terminal of the battery 23. When, however, a regenerative feed back path is provided by virtue of the approach of another vehicle having the same equipment as Fig. 2, the current through the relay I9 will increase to such an extent that its armature will be attracted tothe core of the relay `against the tension of the spring 2I so as to break the circuit through the amber lamp 22 and complete a path through the lower contacts of the armature of relayv I9 in order to light the green lamp 24. It should be noted 4at this time that the path to light the green lamp A24 not only includes the contacts associated with the armature of relay I9 but also includes the upper contacts associated with the relay 20. The green lamp 24 will thus light so long as the regenerative feed back path is such that the intensity of output does not exceed a predetermined value to operate the relay 20. When, however, the intensity of output increases to an extent which will operate the relay 20 which will occur when the two planes have approached quite close 'to one another, the armature of relay 2D will break the circut for the green lamp 24 and will complete'a circuit to light the red lampr 25' over an obviouspath.

As an example of therange of distance within which the relays I9 and 29 will function, the apparatus may bedesigned and suitably biased by adjusting the gainiof the vacuum' tubes, such that a regenerativeieed back path suicient to operate theY relay `I9 but not to operate the relay 20 must take place within a range of between 7500 and 5000 yards. If the planes approach closer than 5000 yards, then the relay 20 can be madeto' operate to light the red lamp. It should be distinctlyV understood,of coorse, that these distances are given byi way of example only, and that they' may be considerably shortened'or lengthened to suit various 'conditions encountered in practice. As an example, if the principles of the presentinvention are ernployed on trucks in a convoy, naturally the distance mentioned above would be considerably shortened, to be effective, let us Vsay `perhaps within a range of 150 to 75 feet. l

Although the apparatus of Figs.' 1 and 2 have been described with particular reference to the useV of a local oscillator, this'local oscillatorimay, under some circumstances, be .eliminated provided that the gain of, theampliflersis suiliciently high to provide the desiredregenerative feed back path between two similarly equipped vehicles within a desired range `of distances. Fig. 3 shows very schematically a circuit arrangement of the invention which requires no local oscillator. 'I'he amplifiersystem illustrated in box form may, if desiredfbe similar to, the amplier system illustrated in Fig. 2.

The invention has the following advantages: (1) It provides an identification system between two or more moving vehicles within a desired limited range of transmission; (2) it provides a means for determining approximate distances between vehicles; (3) the apparatus is extremely simple and inexpensive to construct; and (4) with properly designed apparatus the normal radiation will be weak or non-existent, thereby lessening or completely eliminating-the possibility of detection by the enemy. In connection with this last advantage, it will be evident that where 15 The present invention not only :finds afieldfof use in connection with combat planes, tbutfalso has application to motor vehicles'foruse-initruck convoys. A difficulty hither-to'experienced inthe use of truck convoys is that certain'trucks llin'a convoy may lose their way vfin 1the-(darlo. By equipping each truck with-equipment 41such as shown in Fig. 2, both for the lfront andthe back of the truck, and by locatingieach ofthe-*antennas in a suitable parabolic reflecton-itfwilllbe evident that the rear equip-ment of` each trucklwill-cooperate with the front equipment of the following truck to provide the desired regenerative -feed back circuit, and by adjustment-of theagfain'in the ampliers, the lampi-indicators will lserver to acquaint the driver of thetruck of .the approximate distance between himself'andfthepreceding vehicle. Fig. 4 illustrates, by-way of example, schematically, howa truck can be equipped with the apparatus of Figs. 2 and 3. also finds use in connection with planes flying in formation. The planes can thus maintain desired distances between one another.

it is to be understood that the term vehicle used in the appended claims includes any movable object which will transport the apparatus of the invention, such as an automobile, plane, ship, person or animal.

What is claimed is:

l. A radiant energy system for use between a pair of stations at least one of which is a vehicle, said stations having amplifiers operating at the same frequency, and input and output antennas .for each amplier arranged to minimize coupling therebetween, whereby the amplifiers of said stations together, within a predetermined distance of each other, constitute a regenerative circuit by virtue of the space radiation between the output antenna of each amplier and the input antenna of the other amplifier.

2. A radiant energy system for use between a pair of vehicles having amplifiers operating at the same frequency, and input and output antennas for each amplifier arranged to minimize coupling therebetween, whereby the amplifiers of said vehicles together. within a predetermined distance of each other, constitute a regenerative circuit by virtue of the space radiation between the output antenna of each amplifier and the input antenna cf the other amplifier, and an indicator coupled to each amplier for indicating when said vehicles are within said predetermined distance.

3. A radiant energy system for use between a pair of vehicles having amplifiers operating at the same frequency, input and output antennas for each amplier arranged to minimize coupling therebetween, and a local oscillator associated with each amplifier to cause a relatively weak radiation from the associated output antenna, whereby said ampliers together, within a predetermined distance of each other, constitute a regenerative circuit by virtue of the space radiation between the output antenna of each amplifier and the input antenna of the other ampliiier.

4. A radiant energy system in accordance with claim l, characterized in this that said vehicles are airplanes, the input and output antennas for each amplifier being mounted vertically on the upper and lower portions of the airplane body.

5. A radiant energy system in accordance with claim 1, characterized in this that said vehicles are automobiles, the input and output antennas The invention* zofioneevehicle beingzmounted'in: the rear cf the automobiletand shielde'dfrom;v one anothenvwhile .y

the input-fand output antennas of' the other :ve-

fhiclexare mounted inthe front ofthe automobile and shielded from one another.

v.'6.A1=radiant energyas'ystem for .use between a .pair .oflvehicles having ampliers ,operating 'at the sameffrequency, 4andinput and output anltermas". for each amplifier .arranged to= minimize coupling therebetween, whereby said ampliiiers together, -within ya Apredetermined distance of "each-other, constitute-.a regenerativecircuitlby vvirtueziofithe space radiation .betweenvthe-'outvput-:antenna of 1 each Vamplifier and-"the input antenna of the other ampliiiengan indicatorccupled tofeachampli-iier for indicating'when -said vehiclesare Awithin -said :predetermined distance,

and another indica-tor coupled' to v each? amplier -foriindicatingwhensaid-vehicles are spacedffrom 'fioneanother by a certain distance within said predetermined distance. l

7. A radiant energy system for use between a pair of vehicles having ampliers operating at the saine frequency, each amplifier comprising av pair of vacuum tubes in cascade and having an input antenna coupled to one vacuum tube and an output antenna coupled to the other vacuum tube, an oscillator coupled to a point between Vthe two vacuum tubes of each amplifier to cause a relatively weak radiation from the output antenna, the antennas of each amplifier being arranged to minimize coupling therebetween, whereby said ampliers together, within a predetermined distance of each other, constitute a regenerative circuit by virtue of the space radiation between the output antenna of each amplifier and the input antenna of the other amplier, and means for detecting the increase inY systems of said pair of vehicles constituting aV regenerative feed back circuit within a predetermined range by virtue of the space radiation between the output antenna of'each multistage amplier andthe input antenna of the other multistage system, relays operatively coupledtoV each multistage amplifier system and operative in response to diiferent degrees of intensity of regeneration, and a visual indicator associated with each relay, whereby said indicators serve to indicate ranges of distance between said vehicles.

9. A radiant energy indicating system for use between a pair of spaced vehicles having similar vacuum tube equipment, the equipment of each vehicle comprising a multistage ampliiier system having an input antenna coupled to the input of oneV stage and an output antenna coupled to the output of another stage, an oscillator for each multistage amplifier system coupled to said system at a point between said stages, said amplifier Y each multistage amplifier system and operative "7 in response to diiierent degrees of intensity of regeneration, and a visual indicator associated with each relay, whereby said indicators serve to indicate ranges of distance between said vehicles.

10. A radiant energy indicating system for use between a pair of spaced vehicles having similar vacuum tube equipment, the equipment of each vehicle comprising a multistage amplier system having an input antenna coupled to the input of one stage and an output antenna coupled to the output of another stage, said iirst stage providing an appreciably smaller gain than said last stage, said amplifier systems of said pair of vehicles constituting a regenerative feed back circuit within a predetermined range by virtue oi' the space radiation between the output Vantenna of each multistage ampliiier and the input antenna of the other multistage system, relays operatively coupled to each multistage amplifier system and operative in response to different degrees of intensity of regeneration, and a visual indicator associated with each relay, whereby said indicators serve to indicate ranges of distance between said vehicles.

11. A radiant energy system for use between a pair of vehicles having amplifiers operating at the same frequency, andan input electromag- 

